Background

I have a a fresh umbrella project with a Phoenix app inside. To create the app I used the following commands:

1. mix new test_app --umbrella
2. cd test_app/apps
3. mix phx.new.web web_interface --no-dashboard --no-ecto --no-gettext --no-mailer
4. cd web_interface
5. Add {Phoenix.PubSub, name: WebInterface.PubSub} to lib/application.ex
6. Inside web_interface folder mix setup
7. mix assets.deploy
8. iex -S mix phx.server

After this last command I am then greeted with:

λ iex -S mix phx.server
03:18:31.953 [info] Running WebInterface.Endpoint with cowboy 2.10.0 at 127.0.0.1:4000 (http)
03:18:32.039 [info] Access WebInterface.Endpoint at http://localhost:4000
[watch] build finished, watching for changes…
Interactive Elixir (1.14.1) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> Browserslist: caniuse-lite is outdated. Please run:
npx update-browserslist-db@latest
Why you should do it regularly: GitHub - browserslist/update-db: CLI tool to update caniuse-lite to refresh target browsers from Browserslist config
iex(1)>
iex(1)> Rebuilding…
iex(1)>
iex(1)> Done in 476ms.
iex(1)>

Which outside of the warning for an outdated package, raises nothing to indicate that a step is missing/failed.

However, when I login into localhost:4000, I see this:

Which clearly means something is wrong.

Why is this happening, and how can I fix it?